Composition with increased stress cracking resistance

ABSTRACT

Provided is a molding composition comprising, based on the total weight of the composition, (A) 50.0% by weight to 99.5% by weight of at least one (co)polymer which is a homopolymer or copolymer of at least 80% by weight of methyl methacrylate, (B) 0.5% by weight to 50.0% by weight of at least one copolymer obtained by polymerization of a monomer, and (C) at least one low molecular weight (meth)acrylate (co)polymer having a solution viscosity in chloroform at 25° C. (ISO 1628—part 6) of less than or equal to 55 ml/g.

The present invention relates to a composition having increased stresscracking resistance and its use.

PRIOR ART

Polymethyl methacrylate (PMMA) compositions have long been used in theautomotive sector, in particular as rear light covers and instrumentcovers. In recent years, this material has also increasingly been usedfor shaped articles coloured so that they are opaque. Applications hereare, inter alia, spoilers, pillar claddings, window guide strips,exterior mirrors and exterior mirror bases.

These PMMA compositions are usually processed by extrusion, coextrusion,injection moulding or multicomponent injection moulding to givemouldings for the outdoor area. In these applications, at least theuppermost layer therefore consists of PMMA. Owing to the stability toweathering and surface hardness of PMMA, said layer protects thematrices underneath.

Since the mouldings are frequently provided with a dark colouring (thePMMA layer itself or the layers underneath), they are heated toconsiderable extent in sunlight. High heat distortion resistance istherefore a requirement with regard to the PMMA composition so that theappropriate climatic tests of the mouldings are passed and no softeningof the moulding occurs.

In addition, the mouldings must have high stress cracking resistance andhigh resistance to chemicals, since these applications often come intocontact with cleaning agents, petrol and other aggressive agents.

Furthermore, the known properties of PMMA compositions or PMMAmouldings, such as processability and mechanical properties, must beretained.

EP 0 508 173 B1 describes the use of polymer blends comprising 55% byweight to 98% by weight of PMMA, 2% by weight to 45% by weight of astyrene-acrylonitrile copolymer (SAN) and optionally further processingauxiliaries for the production of various shaped articles. According tothe description, the PMMA contains at least 80% by weight of methylmethacrylate (MMA) units. In the examples, formation of stress cracks isobserved after 2.1 min to 5.5 min. However, this value is not comparablewith the existing results according to the ESCR test. The Vicatsoftening temperature of an exemplary PMMA-SAN polymer blend is 106° C.

Similarly, EP 0 627 461 B1 discloses a weathering-resistant blendcomprising 49% by weight to 99° A) by weight of PMMA and 0.95% by weightto 50% by weight of SAN and 0.05% by weight to 1% by weight of a certainstabilisation packet. Here too, PMMA contains at least 80% by weight ofMMA units. In the examples, formation of stress cracks is observed after680 s to 750 s. However, this value is not comparable with the existingresults according to the ESCR test. An improvement in the heatdistortion resistance is not described.

JP 03-217446 A2 relates to a blend of a copolymer of aromatic vinylmonomers and (meth)acrylic acids, PMMA and SAN. The blends havecomparatively high heat distortion resistance values (114° C.). However,the transmittance of the mouldings is only 84%.

JP 02-272050 A2 describes a blend having good heat distortion resistanceand impact strength, comprising

-   a) a copolymer of 40% by weight to 90% by weight of MMA, 5% by    weight to 20% by weight of maleic anhydride, 5% by weight to 40% by    weight of styrene and 1% by weight to 15% by weight of C₁₋₄-alkyl    acrylate,-   b) a copolymer of acrylonitrile and aromatic vinyl compounds or an    MMA-C₁₋₄-alkyl acrylate copolymer,-   c) an impact modifier comprising rubber grafted with acrylonitrile    and an aromatic vinyl compound.

The difference between the refractive index of the mixture of componentsa) and b) and that of component c) should be not more than 0.005.Nevertheless, such compositions have a strong dependency of the opticalproperties, in particular the transparency and/or the colour impression,on the temperature.

The application WO 2005/047392A1 discloses a polymer mixture whichcontains the following components:

-   a) a low molecular weight (meth)acrylate (co)polymer, characterized    by a solution viscosity in chloroform at 25° C. (ISO 1628—part 6) of    less than or equal to 55 ml/g,-   b) an impact modifier based on crosslinked poly(meth)acrylates,-   c) a higher molecular weight (meth)acrylate (co)polymer,    characterized by a solution viscosity in chloroform at 25° C. (ISO    1628—part 6) of greater than or equal to 65 ml/g and/or-   d) a further (meth)acrylate (co)polymer differing from a),    characterized by a solution viscosity in chloroform at 25° C. (ISO    1628—part 6) of 50 to 55 ml/g, it being possible for the components    a), b), c) and/or d), each by itself, to be understood as meaning    individual polymers or mixtures of polymers, a), b), c) and/or d)    summing to 100% by weight,    it being possible for the polymer mixture also to contain customary    additives, auxiliaries and/or fillers. On wetting of the surface    with isopropanol, a test specimen produced from the polymer mixture    should have a fracture time greater than 1800 s at constant outer    fibre strain of 0.39% and a fracture time greater than 700 s at    constant outer fibre strain of 0.50%. However, a strong dependency    of the optical properties, in particular the transparency and/or the    colour impression, on the temperature is once again observable.    Furthermore, in particular improved stress cracking resistance and    better processability are desirable.

OBJECT AND ACHIEVEMENT

It was the object of the present invention to provide possibilities forimproving the stress cracking resistance of compositions and ofmouldings. At the same time, as high a heat distortion resistance aspossible and as good optical properties as possible should be achieved.In particular, as small a temperature dependence of the visualappearance of the compositions and of the mouldings as possible wasdesired. Furthermore, mechanical properties which are as good aspossible, processability which is as good as possible and long-termstability and weathering resistance which are as high as possible shouldbe realised. It is also intended to indicate particularly expedientprocesses for the preparation of the novel compositions and mouldingsand particularly advantageous potential uses.

This and further objects which are inevitably derived from or directlyarise out of the above considerations are achieved by a compositionhaving all the features of the present Claim 1. The subclaims relatingback to this claim describe particularly expedient developments of thecomposition, and the further claims relate to particularly advantageousapplications of the composition.

By providing a composition which contains, based in each case on itstotal weight,

-   A) 50.0° A) by weight to 99.5% by weight of at least one    (meth)acrylate (co)polymer and-   B) 0.5° A) by weight to 50.0° A) by weight of at least one copolymer    obtainable by polymerisation of a monomer mixture comprising    -   i. 70% by weight to 92% by weight of a vinylaromatic monomer and    -   ii. 8% by weight to 30% by weight of acrylonitrile or        methacrylonitrile or mixtures thereof and    -   iii. 0% by weight to 22% by weight of at least one further        monomer,        the composition having a haze according to ASTM D1003 of less        than 2.0% at 23° C. and a haze according to ASTM D1003 of less        than 4.0% at 40° C. and the composition containing at least one        (meth)acrylate (co)polymer a) having a solution viscosity in        chloroform at 25° C. (ISO 1628—part 6) of greater than 55 ml/g,        it is possible, in a manner which was not directly foreseeable,        to provide a composition which is outstandingly suitable for the        production of mouldings having improved stress cracking        resistance. The composition can be prepared and processed in a        comparatively simple manner, in particular with relatively        little energy consumption, and also permits the realisation of        demanding part geometries.

At the same time, the articles which can be produced from thecomposition are distinguished by a combination of advantageousproperties:

-   -   They have very good optical properties, in particular high        transparency or colour constancy, and show comparatively little        dependence of the optical appearance on the temperature.    -   They have very high heat distortion resistance.    -   They exhibit outstanding mechanical properties, in particular a        high modulus of elasticity and a comparatively high Vicat        softening temperature.    -   The long-term stability and weathering resistance of the        mouldings is likewise outstanding.

CARRYING OUT THE INVENTION (Meth)Acrylate (Co)Polymer A)

The invention relates to a moulding material which contains at least one(meth)acrylate (co)polymer A). The (meth)acrylate (co)polymer may bepresent both as individual polymer and as a mixture of a plurality ofpolymers.

Properties of the (Meth)Acrylate (Co)Polymer A)

The (meth)acrylate (co)polymer or (co)polymers is or are preferablychosen in the proportions and in the composition so that a test specimenproduced from the (meth)acrylate (co)polymer or (co)polymerssimultaneously has the following properties:

-   -   I. a tensile modulus (ISO 527) of at least 2600 MPa, preferably        at least 2750 MPa, particularly preferably at least 2850 MPa, in        particular at least 3000 MPa,    -   II. a Vicat softening temperature VST (ISO 306-B50) of at least        109° C., preferably at least 110° C., particularly preferably at        least 112° C., in particular in the range from 110° C. to 125°        C.,    -   III. a tensile strength (ISO 179-2D, flatwise) of at least 17        kJ/m², preferably at least 18 kJ/m², preferably at least 20        kJ/m², particularly preferably at least 25 kJ/m², in particular        at least 30 kJ/m²,    -   IV. a melt volume flow rate MVR (ISO 1133, 230° C./3.8 kg) of at        least 1.5 cm³/10 min, preferably at least 1.65 cm³/10 min,        particularly preferably at least 2.0 cm³/10 min, in particular        at least 3.0 cm³/10 min.

Customary additives, auxiliaries and/or fillers are expediently chosenso that the above mentioned property profile is as far as possible notadversely affected or is at most slightly adversely affected.

Further Properties

Furthermore, the (meth)acrylate (co)polymer or (co)polymers is or arepreferably present in the proportions and in the composition such that atest specimen produced from the (meth)acrylate (co)polymer or(co)polymers also has at least some of the following properties:

Intrinsic Colour

Light transmittance T_(D65) according to DIN 5033/7 of at least 50%,preferably at least 55%.

Yellowness Index

The yellowness index, determinable according to DIN 6167 (illuminantD65, 10° on 3 mm layer thickness), should preferably be less than 20,preferably less than 17.

Stress Cracking Resistance (ESCR Method)

Fracture time on wetting of the surface with isopropanol and withconstant outer fibre strain of

-   -   0.39%: >1800 s    -   0.50%: >700 s        Surface gloss    -   R(60°): >48%, preferably >50%

According to the invention, the composition is distinguished, interalia, in that it contains at least one (meth)acrylate (co)polymer a)having a solution viscosity in chloroform at 25° C. (ISO 1628—part 6) ofgreater than 55 ml/g, preferably greater than or equal to 65 ml/g, inparticular in the range from 68 ml/g to 75 ml/g.

This may correspond to a molecular weight M_(w) (weight average) of160000 g/mol (determination of M_(w) by means of gel permeationchromatography using polymethyl methacrylate as a calibration standard).The determination of the molecular weight M_(w) can be effected, forexample, by gel permeation chromatography or by a light scatteringmethod (cf. H. F. Mark et al., Encyclopedia of Polymer Science andEngineering, 2nd. Edition, Vol. 10, page 1 et seq., J. Wiley, 1989).

In a first very particularly preferred variant of the present invention,the (meth)acrylate (co)polymer a) is a copolymer of methyl methacrylate,styrene and maleic anhydride.

Suitable proportions may be, for example:

50% by weight to 90% by weight, preferably 70% by weight to 80% byweight, of methyl methacrylate,10% by weight to 20% by weight, preferably 12% by weight to 18% byweight, of styrene and5% by weight to 15% by weight, preferably 8% by weight to 12% by weight,of maleic anhydride.

Corresponding copolymers can be obtained in a manner known per se byfree radical polymerisation. EP-A 264 590 describes, for example, aprocess for the preparation of a moulding material from a monomermixture comprising methyl methacrylate, vinylaromatic, maleic anhydrideand optionally a lower alkyl acrylate, in which the polymerisation iscarried out to a conversion of 50% in the presence or absence of anonpolymerisable organic solvent, and in which the polymerisation iscontinued from a conversion of at least 50% in the temperature rangefrom 75° C. to 150° C. in the presence of an organic solvent to aconversion of at least 80% and then the low molecular weight volatileconstituents are evaporated.

JP-A 60-147 417 describes a process for the preparation of apolymethacrylate moulding material having high heat distortionresistance, in which a monomer mixture comprising methyl methacrylate,maleic anhydride and at least one vinylaromatic is fed into apolymerisation reactor which is suitable for a solution or masspolymerisation, at a temperature of 100° C. to 180° C., and ispolymerised. DE-A 44 40 219 describes a further preparation process.

The proportion of the (meth)acrylate (co)polymer a), based on the totalweight of all (meth)acrylate (co)polymers, is preferably at least 75% byweight, preferably at least 85% by weight, particularly at least 95% byweight.

In a second very particularly preferred variant of the presentinvention, the (meth)acrylate (co)polymer a) is a homopolymer orcopolymer of 80% by weight to 100% by weight, particularly preferably of90% by weight—99.5% by weight, of methyl methacrylate units polymerisedby a free radical method and optionally of 0% by weight—20% by weight,preferably of 0.5% by weight—10% by weight, of further comonomers whichcan be polymerised by a free radical method, e.g. C₁- to C₄-alkyl(meth)acrylates, in particular methyl acrylate, ethyl acrylate or butylacrylate.

Particularly preferred copolymers are those comprising 95% by weight to99.5 by weight of methyl methacrylate and 0.5% by weight to 5% byweight, preferably 1% by weight to 4% by weight, of methyl acrylate.

Expediently, the composition furthermore contains at least one lowmolecular weight (meth)acrylate (co)polymer b) having a solutionviscosity in chloroform at 25° C. (ISO 1628—part 6) of less than orequal to 55 ml/g, preferably less than or equal to 50 ml/g, inparticular 45 ml/g to 55 ml/g.

This may correspond to a molecular weight M_(w) (weight average) of95000 g/mol (determination of M_(w) by means of gel permeationchromatography using polymethyl methacrylate as a calibration standard).The determination of the molecular weight M_(w) can be effected, forexample, by gel permeation chromatography or by a light scatteringmethod (cf. H. F. Mark et al., Encyclopedia of Polymer Science andEngineering, 2nd. Edition, Vol. 10, page 1 et seq., J. Wiley, 1989).

The (meth)acrylate (co)polymer b) is preferably a copolymer of methylmethacrylate, styrene and maleic anhydride.

Suitable proportions may be, for example:

50% by weight to 90% by weight, preferably 70% by weight to 80% byweight, of methyl methacrylate,10% by weight to 20% by weight, preferably 12% by weight to 18% byweight, of styrene and5% by weight to 15% by weight, preferably 8% by weight to 12% by weight,of maleic anhydride.

Valuable information on the preparation of such copolymers can beobtained, inter alia, from EP-A 264 590, JP-A 60-147 417 and DE-A 44 40219.

The (meth)acrylate (co)polymer b) can be prepared, for example, byadding 1.9 g of tert-butyl perneodecanoate and 0.85 g oftert-butylperoxy-3,5,5-trimethylhexanoate as a polymerisation initiatorand 19.6 g of 2-mercaptoethanol as a molecular weight regulator and 4.3g of palmitic acid to a monomer mixture comprising, for example, 6355 gof methyl methacrylate, 1271 g of styrene and 847 g of maleic anhydride.The resulting mixture can be introduced into a polymerisation chamberand degassed, for example for 10 minutes. Thereafter, polymerisation canbe effected in a water bath, for example for 6 hours at 60° C. and thenfor 30 hours at a water bath temperature of 55° C. After about 30 hours,the polymerisation mixture reaches its maximum temperature of about 126°C. After removal of the polymerisation chamber from the water bath, thepolymer is thermostated appropriately in the polymerisation chamber forabout a further 7 hours, for example at 117° C. in the air in an oven.

The (meth)acrylate (co)polymers a) and b) are advantageously present inthe following ratios which preferably sum to at least 75% by weight,preferably to at least 90% by weight, in particular to 100% by weight,based on the total weight of all of the (meth)acrylate (co)polymers.

(Meth)acrylate (co)polymer a): 25% by weight to 75% by weight,preferably 40 by weight to 60% by weight, in particular 45% by weight to55% by weight, (Meth)acrylate (co)polymer b): 25% by weight to 75% byweight, preferably 40% by weight to 60% by weight, in particular 45% byweight to 55% by weight.

Copolymer B)

In addition to the (meth)acrylate (co)polymer, the moulding materialaccording to the invention contains at least one further copolymer (SANcopolymer) B) which is obtainable by polymerisation of a monomer mixturecomprising

-   i. 70% by weight to 92% by weight, preferably 75% by weight to 82%    by weight, in particular 78% by weight to 81% by weight, of at least    one vinylaromatic monomer and-   ii. 8% by weight to 30% by weight, preferably 18% by weight to 25%    by weight, in particular 19% by weight to 22% by weight, of    acrylonitrile or methacrylonitrile or mixtures thereof,-   iii. 0% by weight to 22% by weight of at least one further monomer.

Particularly suitable vinylaromatic monomers are styrene,α-methylstyrene, tert-butylstyrene, monochlorostyrene and vinyltoluene,particularly preferably styrene and α-methylstyrene.

Furthermore, SAN copolymers having a molecular weight (weight averageM_(w)) of 60 000 g/mol to 300 000 g/mol, preferably of 100 000 g/mol to200 000 g/mol, which were preferably prepared by the process describedin British Patent 14 72 195, have proved to be very particularly useful.The molecular weight is determined in a manner known per se, inparticular by light scattering methods.

The amount of component B), based on the total weight of the mouldingmaterial, is, according to the invention, 0.5% by weight to 50.0% byweight, preferably 20.0% by weight to 40.0% by weight.

The amounts of components A) and B) preferably sum to at least 75% byweight, preferably to at least 90% by weight, in particular to 100% byweight, based on the total weight of the composition.

The preparation of component B) is carried out as a rule by knownpolymerisation processes, such as mass, solution, emulsion or beadpolymerisation. Such processes are described, for example, inKunststoffhandbuch [Plastics Handbook], editors Vieweg and Daumiller,volume V; Polystyrol [Polystyrene], Carl-Hanser-Verlag, Munich 1969,page 124 et seq., and in British Patent 14 72 195.

Customary Additives, Auxiliaries and/or Fillers

The composition according to the invention may also contain customaryadditives, auxiliaries and/or fillers, such as, for example, heatstabilisers, UV stabilisers, UV absorbers, antioxidants, in particularsoluble or insoluble dyes or colourants, provided that the properties ofthe composition according to the invention are not adversely affected bythese additives.

UV Stabilisers and Free Radical Scavengers

Optionally present UV stabilisers are, for example, derivatives ofbenzophenone, the substituents of which, such as hydroxyl and/or alkoxygroups, are generally present in the 2- and/or 4-position. These include2-hydroxy-4-n-octyloxybenzophenone, 2,4-dihydroxybenzophenone,2,2′-dihydroxy-4-methoxybenzophenone,2,2′,4,4′-tetrahydroxybenzophenone,2,2′-dihydroxy-4,4′-dimethoxybenzophenone,2-hydroxy-4-methoxybenzophenone. Furthermore, substituted benzotriazolesare very suitable as an added UV stabiliser and include in particular2-(2-hydroxy-5-methylphenyl)benzotriazole,2-[2-hydroxy-3,5-di(alpha,alpha-dimethylbenzyl)phenyl]benzotriazole,2-(2-hydroxy-3,5-di-tert-butylphenyl)benzotriazole,2-(2-hydroxy-3,5-butyl-5-methylphenyl)-5-chlorobenzotriazole,2-(2-hydroxy-3,5-di-tert-butylphenyl)-5-chlorobenzotriazole,2-(2-hydroxy-3,5-di-tert-amylphenyl)benzotriazole,2-(2-hydroxy-5-tert-butylphenyl)benzotriazole,2-(2-hydroxy-3-sec-butyl-5-tert-butylphenyl)benzotriazole and2-(2-hydroxy-5-tert-octylphenyl)benzotriazole.

UV stabilisers which may furthermore be used are ethyl2-cyano-3,3-diphenylacrylate, 2-ethoxy-2′-ethyloxalic acid bisanilide,2-ethoxy-5-tert-butyl-2′-ethyloxalic acid bisanilide and substitutedphenyl benzoates.

The UV stabilisers may be present as low molecular weight compounds, asstated above, in the polymethacrylate materials to be stabilised.However, UV-absorbing groups in the matrix polymer molecules may also becovalently bonded after copolymerisation with polymerisable UV-absorbingcompounds, such as, for example, acrylic, methacrylic or allylderivatives of benzophenone derivatives or benzotriazole derivatives.

The proportion of UV stabilisers, it also being possible for this to bemixtures of chemically different UV stabilisers, is as a rule from 0.01%by weight to 1.0% by weight, especially from 0.01% by weight to 0.5% byweight, in particular from 0.02% by weight to 0.2% by weight, based onthe totality of all constituents of the polymethacrylate resin accordingto the invention.

Sterically hindered amines, which are known by the name HALS ((HinderedAmine Light Stabiliser) may be mentioned here as an example of freeradical scavengers/UV stabilisers. They can be used for inhibitingageing processes in finishes and plastics, especially in polyolefinplastics (Kunststoffe [Plastics], 74 (1984) 10, pages 620 to 623;Farbe+Lack [Paints+Finishes], 96^(th) year, 9/1990, pages 689 to 693).The tetramethylpiperidine group present in the HALS compounds isresponsible for the stabilising effect thereof. This class of compoundsmay be either unsubstituted or substituted by alkyl or acyl groups onthe piperidine nitrogen. The sterically hindered amines do not absorb inthe UV range. They trap free radicals formed, which once again the UVabsorbers are incapable of doing.

Examples of HALS compounds which have a stabilising effect and can alsobe used as mixtures are: bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate,8-acetyl-3-dodecyl-7,7,9,9-tetramethyl-1,3-8-triazaspiro(4,5)decane-2,5-dione,bis(2,2,6,6-tetramethyl-4-piperidyl)succinate, poly(N-

-hydroxyethyl-2,2,6,6-tetramethyl-4-hydroxypiperidine succinic acidester) and bis(N-methyl-2,2,6,6-tetramethyl-4-piperidyl)sebacate.

The free radical scavengers/UV stabilisers are used in the compositionsaccording to the invention in amounts of 0.01% by weight to 1.5% byweight, especially in amounts of 0.02% by weight to 1.0% by weight, inparticular in amounts of 0.02% by weight to 0.5% by weight, based on thetotality of all constituents.

Lubricants or Mould Release Agents

In particular, lubricants or mould release agents which can reduce orcompletely prevent possible adhesion of the moulding material to theinjection mould are important for the injection moulding process.

Accordingly, lubricants, for example selected from the group consistingof the saturated fatty acids having less than C₂₀, preferably C₁₆ toC₁₈, carbon atoms or of the saturated fatty alcohols having less thanC₂₀, preferably C₁₆ to C₁₈, carbon atoms, may be present as auxiliaries.Small proportions of not more than 0.25% by weight, e.g. 0.05% by weightto 0.2% by weight based on the moulding material, are preferablypresent.

For example, stearic acid, palmitic acid and industrial mixtures ofstearic and palmitic acid are suitable. For example, n-hexadecanol,n-octadecanol and industrial mixtures of n-hexadecanol and n-octadecanolare furthermore suitable.

A particularly preferred lubricant or mould release agent is stearylalcohol.

Further Additives, Auxiliaries and/or Fillers

In the context of the present invention, the addition of the componentsc₁), c₂), c₃) and/or c₄) has also proved very particularly useful.

The component c₁) designates triaryl phosphites of the general formula(I)

in which R¹ and R² represent C₁-C₁₂-alkyl, such as methyl, ethyl,propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl,1,1-dimethylethyl, n-pentyl, 1-methylbutyl, 2-methylbutyl,3-methylbutyl, 1,2-dimethylpropyl, 1,1-dimethylpropyl,2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 1-methylpentyl,2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,2-dimethylbutyl,1,3-dimethylbutyl, 2,3-dimethylbutyl, 1,1-dimethylbutyl,2,2-dimethylbutyl, 3,3-dimethylbutyl, 1,1,2-trimethylpropyl,1,2,2-trimethylpropyl, 1-ethylbutyl, 2-ethylbutyl,1-ethyl-2-methylpropyl, n-heptyl, 1-methylhexyl, 2-methylhexyl,3-methylhexyl, 4-methylhexyl, 5-methylhexyl, 1-ethylpentyl,2-ethylpentyl, 1-propylbutyl, octyl, nonyl, decyl, undecyl and dodecyl,preferably C₃-C₁₂-alkyl radicals branched in 1-position (a), inparticular C₃-C₇-alkyl radicals, such as 1-methylethyl, 1-methylpropyl,1,1-dimethylethyl, 1-methylbutyl, 1,2-dimethylpropyl,1,1-dimethylpropyl, 1-ethylpropyl, 1-methylpentyl, 1,2-dimethylbutyl,1,3-dimethylbutyl, 1,1-dimethylbutyl, 1,1,2-trimethylpropyl,1,2,2-trimethylpropyl, 1-ethylbutyl, 1-ethyl-2-methylpropyl,1-methylhexyl, 1-ethylpentyl and 1-propylbutyl and1,1,3,3-tetramethylbutyl, 1,1,2,2,5,5-hexamethylhexyl,C₅-C₈-cycloalkyl, such as cyclopentyl, cyclohexyl, cycloheptyl andcyclooctyl, preferably cyclohexyl,C₆-C₁₀-aryl and C₆-C₁₀-aryl-C₁-C₄-alkyl, the aryl radicals of which maybe up to trisubstituted by C₁-C₄-alkyl, such as phenyl, naphthyl or2,2-dimethylbenzyl, and R³ denotes hydrogen and C₁-C₄-alkyl, such asmethyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl andtert-butyl, preferably hydrogen and methyl.

Examples of compounds (I) which are particularly important with regardto the present invention are the commercially availabletris(2,4-di-tert-butylphenyl) phosphite (Irgafos™ 168, Ciby-Geigy) andtris(nonylphenyl)phosphite, preferablytris(2,4-di-tert-butylphenyl)phosphite.

The component c₂) designates an amine of the general formula (II)

in which n represents the values 2 to 10, preferably 2 to 8. Compoundsof this type are also known by the designation HALS (hindered aminelight stabilisers) compounds and are commercially available.

An example of compounds (II) which are particularly important withregard to the present invention is bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate (commercially available by the name Tinuvin™ 770 DF (CibaGeigy)).

The component c₃) designates a benzotriazole of the general formula(III)

in which R⁴, R⁵ and R⁶ have the meaning of R¹.

Examples of compounds (III) which are particularly important with regardto the present invention are2-(2′-hydroxy-5′-methyl-phenyl)benzotriazole (commercially available bythe name Tinuvin™ P (Ciba Geigy)) or2-(2′-hydroxy-3′-dodecyl-5′-methyl-decyl)benzotriazole.

The component c₄) designates a phenol of the general formula (IV)

AB_(k)  (IV)

in which k denotes 1, 2 or 4 and, if k is 1, A represents —COOR⁷,—CONHR⁷,

R⁷ denoting C₁-C₂₁-alkyl and,if k is 2, A representing —CONH—(CH₂)_(n)—CONH—,

in which p and m denote integers from 1 to 10 and, if k is 4, Arepresents

in which q denotes an integer from 1 to 4, andB represents

in which R⁸ and R⁹ represent hydrogen, methyl or tert-butyl.

The addition of the component c₄) may in some cases lead to a furtherimprovement of the stress cracking resistance after weathering.

Examples of compounds (IV), which are particularly important with regardto the present invention, are octadecyl3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (commercially availableby the name Irganox™ 1076 (Ciba Geigy)) and

The components c₁), c₂) and c₃) are preferably used as a mixture inorder to achieve a synergistic effect with regard to the improvement ofthe stress cracking resistance after weathering.

The preferred amounts of the components c₁) to c₃) are in each case inthe range from 1% by weight to 50% by weight, preferably from 30% byweight to 50% by weight, based on the sum of the amounts of thecomponents c₁) to c₃), the individual amounts summing to 100.

The amount of the component c₄) is preferably chosen in the range from0% by weight to 25% by weight, preferably in the range from 10% byweight to 25% by weight, based on the total amount of the components c₁)to c₃).

The total amount of the components c₁) to c₄), based on the total weightof the composition, is advantageously 0.05% by weight to 1% by weight,preferably 0.1% by weight to 0.5% by weight.

Opacity (Haze) of the Composition

According to the invention, the composition is characterized in that ithas a haze according to ASTM D1003 of less than 2.0%, preferably lessthan 1.5%, in particular less than 1.2%, at 23° C. and a haze accordingto ASTM D1003 of less than 4.0%, preferably less than 3.5%, inparticular less than 3.0%, at 40° C. The haze according to ASTM D1003 at60° C. is expediently less than 6.0%, preferably less than 5.5%, inparticular less than 5.0%.

The addition of additives, such as, for example, impact modifiers,having substantially different thermal behaviour of the refractiveindices compared with the polymer matrix, should therefore as far aspossible be avoided since otherwise a significant temperature dependenceof the optical appearance is observable.

Transparency of the Composition

Furthermore, the composition preferably has a light transmittanceT_(D65) according to DIN 5033/7 greater than 80%, preferably greaterthan 83%, in particular greater than 85%, both at 23° C. and at 40° C.

Melt Volume Flow Rate MVR of the Moulding Material

In the present invention, the composition preferably has a melt volumeflow rate MVR measured according to ISO 1133 at 230° C. and 3.8 kg, ofgreater than 1.2 cm³/10 min, preferably of greater than 1.5 cm³/10 min,in particular in the range from 1.7 cm³/10 min to 4.0 cm³/10 min.

Preparation of the Composition

The composition can be prepared by dry blending of the components, whichmay be present as powder, particles or preferably granules

The composition can also be processed by melting and mixing theindividual components in the molten state or by melting dry premixes ofthe individual components to give a ready-to-use moulding material. Thiscan be effected, for example, in single-screw or twin-screw extruders.The extrudate obtained can then be granulated. Customary additives,auxiliaries and/or fillers can be directly admixed or added later by endusers as required.

Processing to Give Mouldings

The composition according to the invention is suitable as a startingmaterial for the production of mouldings having improved resistance tochemicals and stress cracking resistance. The forming of the compositioncan be effected by methods known per se, for example by processing viathe elastoviscous state, i.e. by kneading, rolling, calendering,extrusion or injection moulding, extrusion and injection moulding, inparticular injection moulding, being particularly preferred here.

The injection moulding of the composition can be effected in a mannerknown per se at temperatures in the range of 220° C.-260° C. (melttemperature) and a mould temperature of preferably 60° C. to 90° C.

The extrusion is preferably carried out at a temperature of 220° C. to260° C.

Mouldings

The mouldings obtainable in this manner are distinguished in that theyhave a haze according to ASTM D1003 of less than 2.0%, preferably lessthan 1.5%, in particular less than 1.2%, at 23° C. and a haze accordingto ASTM D1003 of less than 4.0%, preferably less than 3.5%, inparticular less than 3.0%, at 40° C. The haze according to ASTM D1003 at60° C. is expediently less than 6.0%, preferably less than 5.5%, inparticular less than 5.0%.

Furthermore, the mouldings preferably show a light transmittance,T_(D65) according to DIN 5033/7 in the range of 40% to 93%, inparticular in the range of 70% to 92%.

The yellowness index of the mouldings, determinable according to DIN6167 (illuminant D65, 10° on 3 mm layer thickness) should preferably beless than 6, preferably less than 7.

The Vicat softening temperature of the mouldings according to ISO306-B50 is advantageously at least 109° C., preferably at least 112° C.

The nominal elongation at break of the mouldings according to ISO 527should preferably be at least 3.0%, particularly preferably 3.2%.

The modulus of elasticity of the mouldings according to ISO 527 isadvantageously greater than 3200 MPa, preferably 3500 MPa.

Furthermore, particularly suitable mouldings have a normalised stresscracking resistance factor greater than 0.80 in the stress crackingresistance test according to the ESCR method at an outer fibre strain of1% after 30 minutes.

Uses

The mouldings according to the invention can be used in particular as acovering, finish or film. Injection mouldings can be used as parts ofhousehold appliances, communication devices, hobby or sports devices,bodywork parts or parts of bodywork parts in automotive, ship oraircraft construction. Typical examples of bodywork parts or parts ofbodywork parts of automobiles are, for example, spoilers, claddings,roof modules or exterior mirror housings.

EXAMPLES

The invention is explained in more detail below by examples, without itbeing intended to limit the concept of the invention thereby.

The following components a1), a2), b) and/or c) were used for thepolymer matrix.

The following was used as component a1): a commercially availablecopolymer of 75% by weight of methyl methacrylate, 15% by weight ofstyrene and 10% by weight of maleic anhydride, having a solutionviscosity number according to ISO 1628-6 at 25° C. in chloroform of 68ml/g.

The following was used as component (a2): a commercially availablecopolymer of 99% by weight of methyl methacrylate and 1% by weight ofmethyl acrylate, having a solution viscosity in chloroform at 25° C.(ISO 1628—part 6) of about 72 ml/g.

Preparation of Component b):

1.9 g of tert-butyl perneodecanoate and 0.85 g of tert-butylperoxy-3,5,5-trimethylhexanoate as a polymerisation initiator and 19.6 gof 2-mercaptoethanol as a molecular weight regulator and 4.3 g ofpalmitic acid are added to a monomer mixture comprising 6355 g of methylmethacrylate, 1271 g of styrene and 847 g of maleic anhydride.

The resulting mixture is introduced into a polymerisation chamber anddegassed for 10 minutes. Thereafter, polymerisation is effected in awater bath for 6 hours at 60° C. and then for 30 hours at a water bathtemperature of 55° C. After about 30 hours the polymerisation mixturereaches its maximum temperature of 126° C. After removal of thepolymerisation chamber from the water bath, the polymer is thermostatedin the polymerisation chamber for a further 7 hours at 117° C. in air inan oven.

The resulting copolymer is clear and virtually colourless and has a V.N.(solution viscosity number according to ISO 1628-6, 25° C., chloroform)of 48.7 ml/g. The flowability of the copolymer was determined accordingto ISO 1133 at 230° C. and 3.8 kg with MVR=3.27 cm³/10 min.

The component b) is thus a copolymer of 75% by weight of methylmethacrylate, 15% by weight of styrene and 10% by weight of maleicanhydride.

The following was used as component c): a commercially availablecopolymer of 99% by weight of methyl methacrylate and 1% by weight ofmethyl acrylate, having a solution viscosity in chloroform at 25° C.(ISO 1628—part 6) of about 53 ml/g.

®TYRIL 905UV from Dow Plastics was used as the SAN copolymer.

A dry blend was prepared from the individual components by means of atumbling mixer and was then compounded on a Leistritz LSM 30/34twin-screw extruder.

The compositions of the individual examples are documented in Table 1.

TABLE 1 Polymer matrix  ®TYRIL 905UV [% by weight] [% by weight] ExampleB1 Component a1) (70) 30 Comparative example Component a1) (100) VB1Example B2 Component a2) (35) 30 Component b) (35) Comparative exampleComponent b) (50) VB2 Component c) (50) Comparative example Component b)(35) 30 VB3 Component c) (35)

The melt volume flow rate MVR (test standard ISO 1133: 1997) wasdetermined.

On an injection moulding machine Battenfeld BA 350 CD, tensile test barsand injection moulded discs were produced from all materials and testedwith regard to their properties by the following methods:

Vicat (16 h/80° C.): Determination of the Vicat softening temperature(test standard DIN ISO 306: August 1994) Modulus of elasticity:Determination of the modulus of elasticity (test standard: ISO 527-2)Tensile strength: Determination of the elongation at break (teststandard: ISO 527) Light transmittance T_(D65) according to DIN 5033/7,23° C. Yellowness index: according to DIN 6167 (illuminant D65, 10° on 3mm layer thickness, 23° C.) Haze: according to ASTM D1003

Stress Crack Formation (ESCR):

Before the test, all samples were stored for at least 24 h at 23° C./50%relative humidity.

In the ESCR test according to Prof. Bledzki (A. Bledzki, C. Barth,Materialprufung [Material Testing] 40, 10 (1998)), an outer fibre strainwhich was constant as a function of time was applied by means of athree-point bending arrangement. The test specimen (dimensions 80 mm×20mm×d, thickness d=4 mm) rested flat on two supports with a spacing L of64 mm.

The specific experimental setup is illustrated in FIGS. 1 and 2. FIG. 1schematically shows the three-point bending arrangement in the ESCRtest. FIG. 2 shows an ESCR test apparatus (the arrangement from FIG. 1is upside down here). The cylindrical supports and the crossbeam have aradius of 10 MM.

The necessary sag s at a given outer fibre strain £ (in the middle ofthe test specimen on the side opposite the crossbeam) was calculated asin ISO 178 according to:

$\begin{matrix}{ɛ = \frac{6\; {sd}}{L^{2}}} & (1)\end{matrix}$

The sag s was adjusted by means of a knurled screw. ε was adjusted to avalue of 1%. After approaching the outer fibre strain (T₀), a hold timeof 2 min was allowed in order to await the first relaxation phenomena.At T=T₁=2 min, the filter paper already placed on top beforehand in themiddle and having the dimensions 50×10 mm² was wetted with the medium(isopropanol). The force which was required for maintaining the outerfibre strain was measured from T₁ as a function of time. The filterpaper was kept constantly moist with the medium in the course of themeasurement. The measurement was terminated on breaking of the testspecimen (force=0) but after 30 min at the latest.

This process was repeated for three test specimens. For comparison, theforce curve was also recorded for a test specimen which was exposed tothe same outer fibre strain but no medium. In the case of the sampleswithout influence of the medium, the measured force value decreasedslowly whilst the samples which are tested on the influence of themedium showed a faster decrease in force depending on resistance.

The time-dependent measure of the stress cracking resistance E_(T)^(norm) is obtained in this experiment from the ratio of the forcesF_(r) ^(mM) required for maintaining the outer fibre strain and F_(T)^(oM) without influence of the medium:

$\begin{matrix}{E_{T}^{norm} = \frac{F_{T}^{mM} \cdot F_{T\; 1}^{oM}}{F_{T\; 1}^{mM} \cdot F_{T}^{oM}}} & (2)\end{matrix}$

Here, the forces are additionally based on their value at T₁ so that attime T₁: E_(T) ^(norm)=1. Three curves are a result in the diagram, foreach test specimen with influence of the medium. The reference in eachcase is the same measurement for the test specimen without the influenceof the medium. Normalised ESCR factors close to 1 characterize good ESCresistance, and sharply decreasing values at E_(T) ^(norm) over time Tcharacterize poor resistance. Results of the tests on the mixtures andthe corresponding shaped articles are shown in Table 2.

TABLE 2 B1 VB1 B2 VB2 VB3 Vicat [° C.] 115.5 119 113.2 115 110.3 MVR[ml/10 min] 1.9 1.9 2.9 4.5 5.2 ESCR [min] No break - >40 No break -0.08-0.42 2.6-3.9 continuous continuous decrease decrease 0.92 at 0.85at 30 min 30 min Modulus of 3600 3702 3500 elasticity [MPa] Elongationat 3.5 3.4 3.1 break [%] T_(D65) [%] 90 89.4 91 Yellowness −0.4 5.490.08 index [ ] Haze [%] 1.61 0.61 0.54

1-27. (canceled) 28: A molding composition comprising, based on thetotal weight of the composition: A) 50.0% by weight to 99.5% by weightof at least one (co)polymer which is a homopolymer or copolymer of atleast 80% by weight of methyl methacrylate and optionally up to 20% byweight of further monomers copolymerizable with methyl methacrylate, B)0.5% by weight to 50.0% by weight of at least one copolymer obtained bypolymerization of a monomer mixture comprising: I 70% by weight to 92%by weight of a vinylaromatic monomer, and Ii 8% by weight to 30% byweight of acrylonitrile or methacrylonitrile or mixtures thereof, andIii 0% by weight to 22% by weight of at least one additional monomer,and C) at least one low molecular weight (meth)acrylate (co)polymerhaving a solution viscosity in chloroform at 25° C. (ISO 1628—part 6) ofless than or equal to 55 ml/g, wherein the composition has a hazeaccording to ASTM D1003 of less than 2.0% at 23° C. and a haze accordingto ASTM D1003 of less than 4.0% at 40° C., the composition comprises atleast one copolymer A) having a solution viscosity in chloroform at 25°C. (ISO 1628—part 6) of greater than 55 ml/g, and a molding obtainedfrom the composition has a Vicat-Softening Temperature measuredaccording to ISO 306-B50 of at least 109° C.
 29. The composition ofclaim 28, wherein the (co)polymer A) has a solution viscosity inchloroform at 25° C. (ISO 1628—part 6) of greater than or equal to 65ml/g.
 30. The composition of claim 28, wherein the copolymer B) isobtainable by polymerization of a monomer mixture comprising: 175% byweight to 92% by weight of a vinylaromatic monomer and Ii 18% by weightto 25% by weight of acrylonitrile or methacrylonitrile or mixturesthereof.
 31. The composition of claim 28, wherein the (co)polymer A) isa copolymer of methyl methacrylate, styrene and maleic anhydride. 32.The composition of claim 31, wherein the (co)polymer A) is a copolymerof: 50% by weight to 90% by weight of methyl methacrylate, 10% by weightto 20% by weight of styrene, and 5% by weight to 15% by weight of maleicanhydride.
 33. The composition of claim 31, which comprises the acrylate(co)polymer A) in an amount of at least 75% by weight, based on thetotal weight of all (meth)acrylate (co)polymers.
 34. The composition ofclaim 28, wherein the (co)polymer A) is a copolymer of 95% by weight to99.5% by weight of methyl methacrylate and 0.5% by weight to 5% byweight of methyl acrylate.
 35. The composition of claim 28, wherein the(meth)acrylate (co)polymer C) is a copolymer of methyl methacrylate,styrene and maleic anhydride.
 36. The composition of claim 35, whereinthe (meth)acrylate (co)polymer C) is a copolymer of: 50% by weight to90% by weight of methyl methacrylate, 10% by weight to 20% by weight ofstyrene, and 5% by weight to 15% by weight of maleic anhydride.
 37. Thecomposition of claim 28, wherein the (co)polymer A) and the(meth)acrylate (co)polymer C) are present in the following ratios, basedon the total weight of the (meth)acrylate (co)polymers: A) 25% by weightto 75% by weight C) 25% by weight to 75% by weight.
 38. The compositionof claim 28, further comprising at least one lubricant as an auxiliary.39. The composition of claim 38, comprising stearyl alcohol as a moldrelease agent.
 40. The composition of claim 28, wherein the compositionhas a melt volume flow rate MVR, measured according to ISO 1133 at 230°C. and 3.8 kg, of greater than 1.2 cm³/10 min.
 41. The composition ofclaim 28, which is in the form of granules.
 42. The composition of claim28, which has a light transmittance TD65 according to DIN 5033/7 greaterthan 80% both at 23° C. and at 40° C.
 43. The composition of claim 28,which has a haze according to ASTM D1003 of less than 3.0% at 40° C. 44.The composition of claim 28, which has a haze according to ASTM D1003 ofless than 6.0% at 60° C.
 45. The composition of claim 28, wherein amolding obtained from the composition has a Vicat-Softening Temperaturemeasured according to ISO 306-B50 of at least 112° C.
 46. A process forproducing a molding, comprising forming a molding from the compositionof claim
 28. 47. The process of claim 46, wherein the composition isextruded or injection molded.
 48. A molding produced by a process ofclaim 46, wherein the molding has a haze according to ASTM D1003 of lessthan 2.0% at 23° C. and a haze according to ASTM D1003 of less than 4.0%at 40° C.
 49. The molding of claim 48, which has a light transmittanceTD65 according to DIN 5033/7 in the range of 40% to 93% and a yellownessindex according to DIN 6167 of less than
 6. 50. The molding of claim 48,which has at least one of the following properties: (a) a Vicatsoftening temperature according to ISO 306-B50 of at least 109° C., (b)a nominal elongation at break according to ISO 527 of at least 3.0%, and(c) a modulus of elasticity according to ISO 527 of greater than 3200MPa.
 51. The molding of claim 48, which has a normalized stress crackingresistance factor greater than 0.80 in the stress cracking resistancetest according to the ESCR method after 30 minutes at an outer fiberstrain of 1%.